inpcom.c: MS Windows abs pathname may begin with
/ or \ or d:\ or d:/
If variable 'mingwpath' is set in .spinit, also with /d/
tiny
use inp_pathresolve_at() for `.inc' files too
test files for `.inc'
tst absolute too
fix inp_pathresolve() semantic

fixme, sourcepath shouldn't be preset with '.'
inpcom.c: MSVC compatibility
make expand_section_references() independent from availability of '.end'